The present invention relates to an oscillator circuit comprising three inverter stages or bistable circuits connected in cascade, and more particularly to such an oscillator circuit having timing circuitry for controlling the period of oscillations and the duty cycle of the oscillations.
Oscillator circuits are used for energizing smoke sensors in fire detecting systems. A known oscillating circuit for this purpose is disclosed in U.S. Pat. No. 3,773,596. For proper operation this oscillator requires the use of a pair of matched field effect transistors. Moreover, this oscillator does not provide for a simple manner of changing the duty cycle of its output pulse signal in order to meet the accuracy requirements of a particular fire detecting system. It would be desireable to eliminate the requirement for a matched pair of transistors and to be able to easily select output pulse period and duty cycle.